DESCRIPTION

These functions provide an interface for managing dynamically created
oids. The sysctl context is responsible for keeping track of created
oids, as well as their proper removal when needed. It adds a simple
transactional aspect to oid removal operations; i.e., if a removal
operation fails part way, it is possible to roll back the sysctl tree to
its previous state.
The sysctl_ctx_init() function initializes a sysctl context. The clist
argument must point to an already allocated variable. A context must be
initialized before use. Once it is initialized, a pointer to the context
can be passed as an argument to all the SYSCTL_ADD_* macros (see
sysctl_add_oid(9)), and it will be updated with entries pointing to newly
created oids.
Internally, the context is represented as a queue(3) TAILQ linked list.
The list consists of struct sysctl_ctx_entry entries:
struct sysctl_ctx_entry {
struct sysctl_oid *entry;
TAILQ_ENTRY(sysctl_ctx_entry) link;
};
TAILQ_HEAD(sysctl_ctx_list, sysctl_ctx_entry);
Each context entry points to one dynamic oid that it manages. Newly
created oids are always inserted in the front of the list.
The sysctl_ctx_free() function removes the context and associated oids it
manages. If the function completes successfully, all managed oids have
been unregistered (removed from the tree) and freed, together with all
their allocated memory, and the entries of the context have been freed as
well.
The removal operation is performed in two steps. First, for each context
entry, the function sysctl_remove_oid(9) is executed, with parameter del
set to 0, which inhibits the freeing of resources. If there are no
errors during this step, sysctl_ctx_free() proceeds to the next step. If
the first step fails, all unregistered oids associated with the context
are registered again.
Note: in most cases, the programmer specifies OID_AUTO as the oid number
when creating an oid. However, during registration of the oid in the
tree, this number is changed to the first available number greater than
or equal to CTL_AUTO_START. If the first step of context deletion fails,
re-registration of the oid does not change the already assigned oid
number (which is different from OID_AUTO). This ensures that re-
registered entries maintain their original positions in the tree.
The second step actually performs the deletion of the dynamic oids.
sysctl_remove_oid(9) iterates through the context list, starting from
beginning (i.e., the newest entries). Important: this time, the function
not only deletes the oids from the tree, but also frees their memory
(provided that oid_refcnt == 0), as well as the memory of all context
entries.
The sysctl_ctx_entry_add() function allows the addition of an existing
dynamic oid to a context.
The sysctl_ctx_entry_del() function removes an entry from the context.
Important: in this case, only the corresponding struct sysctl_ctx_entry
is freed, but the oidp pointer remains intact. Thereafter, the
programmer is responsible for managing the resources allocated to this
oid.
The sysctl_ctx_entry_find() function searches for a given oidp within a
context list, either returning a pointer to the structsysctl_ctx_entry
found, or NULL.

SEEALSO

HISTORY

AUTHORS

BUGS

The current removal algorithm is somewhat heavy. In the worst case, all
oids need to be unregistered, registered again, and then unregistered and
deleted. However, the algorithm does guarantee transactional properties
for removal operations.
All operations on contexts involve linked list traversal. For this
reason, creation and removal of entries is relatively costly.